Boil the cauliflower and potato in salted water for 15 minutes.Drain and keep aside
Marinate the prawns with 1/2 tsp turmeric powder and 1/2 tsp salt for 10-15 mins.
Heat 4 tbsp oil in a kadhai and fry the cauliflower and potato pieces till it nicely colored and half cooked. Add 1/2 tsp turmeric and pinch of salt while frying. Remove the fried vegetables when done and keep aside.
Add oil in a kadhai if required or you can continue with the same oil if you are left with avoid using extra oil. Fry the prawns. Remove the fried prawns and keep aside.
In the same kadhai add little oil if required. Fry the grated onion till light brown along with sugar . Now add the ginger garlic paste and fry for another 10-15 mins. Add all the powder accept the garam masala and fry the mixture for another 5-7 mins.Now mix the half cooked vegetables with the gravy and saute for another 5 mins. Add salt to taste.Add the fried prawns and allow to cook with covered lid.When the vegetables are soft, add the garam masala and mix well. Turn off the heat.